The present invention relates generally to transversal filters, and more particularly, to an improved passband transversal equalizer.
High rate digital communications systems, such as those that employ digital transmitters, are prone to distortion and intersymbol interference. Conventional baseband and passband transversal filter equalizers have been developed to minimize these problems. However, conventional transversal equalizers are relatively large and heavy and use a relatively large amount of power and exhibit distortion. Conventional transversal equalizers also exhibit relatively low dynamic range and have unwanted mutual interaction between signals.
It is an objective of the present invention to provide for an improved passband transversal equalizer that overcomes limitations found in conventional transversal equalizers.
To accomplish the above and other objectives, the present invention provides for an improved passband transversal equalizer that improves upon conventional transversal equalizers. The passband transversal equalizer uses a novel partitioning of circuits to improve the dynamic range and minimize unwanted signal interactions. The passband transversal equalizer uses a novel interconnection matrix and may be implemented using GaAs monolithic microwave integrated circuit (MMIC) devices for improved performance.
More particularly, the passband transversal equalizer comprises a divider that receives an input signal and splits the input signal along a predetermined number of signal paths. A first plurality of coaxial delay lines delays the signals propagating along the respective signal paths by a first set of nominal relative delays. A plurality of active divider having push-pull outputs is respectively coupled to outputs of each of the coaxial delay lines. An interconnection matrix couples one of the outputs of the active divider to one of a plurality of complex weighting and combiner circuits. A second plurality of coaxial delay lines, which delay the respective signals by a second set of nominal relative delays, are respectively coupled to the complex weighting and combiner circuits. A combiner combines the signals to produce an equalized output.
The passband transversal equalizer provides the following advantages. Transmission lines in the interconnection matrix exhibit low VSWR and minimal mutual interaction. The coaxial delay lines exhibit low VSWR and no mutual interaction. The equalizer has evenly distributed gain that increases its dynamic range and avoids problems with feedback and crosstalk. Using different delay lines easily customizes the tap delays.